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Dec. 10, 1929. s. MORSE ELECTRIC HEATER Filed Sept. 24, 1927 2 Sheets-Sheet (1Mo: new

Dec. 10, 1929. s. MORSE ELECTRIC HEATER Filed Sept. 24, 1927 2 Sheets-Sheet 2 Patented Dec. 10, 1929 .s'TER'NE MoRsE, 0F cIlEVELANn HEIGH'rsfoHIo i ELECTRIC "fepisiieation medfsebteinlier 24, 1927. serial No. 22256.

.Thisdeviceis -ra specific .'embodimen'tofthe 'general' 'principles l,disclosed inamy' fcopending zapplicatin zSerialuNo. :86,413 filed .February, .1926,rand represents improvements .35 inthe-devcesithe'rein disclosed. l .These iimprovementsahave ffo'r one-fobject the xprovision of improved means for'rfconducting heat; frornthe heating element to the bodyofthe-device. r A

A further objectisiafconstructionsuch that the `resistor blocks xwill :be retained at all timesin-fsubstantial' physical contact with the containing member Whetherorfnot pressure is being exerted upon them longitudinally.- A further object is the provision of-an adequate'type of. insulation which is adaptable to non-ferrous'pcontaining.members such as aluminum, vwhich f-iszmechanically ;unyield ing and substantially incompressible, 'which maybeeasily renewed, and zwhich, `b'einglaterally1flexible, .responds/to fthel thermal expansion of the'cntaining .member however large it maybe. .i i' if .1:

A further Objectis the'gp'rovision'ioffacomf bined insulation 'and Aparallel'substantially fixed resistor `in-connection -with 'the variable resistor. l

A further object is the lprovision of a'substantially fixed series resistance and a substantially fixed parallel resistance in order to prevent the device from taking either too large a'current from the source of energy supply or too small a current for the satisfactory operation of the device. f

A further object is the provision ofa sub. stantially fixed parallel .resistor in subst'antial electrical contact with the variable re-A sistor throughout its length-in order'to equalize the voltage drop throughout the variable 40 resistor.

A further object is the provision of a containing member substantially concavely curved with the resistor lying against the internal curvature of the container in order that the resistor is pressed -rmly against the containing member along its entire length by a component of the longitudinal pressure on the resistor., this pressure being therefore substantially proportional to the current flow and 59 insuring an increase of heat conductivity between' resistor and 'icontaii'ng imember with increase of heat' produced inftheresistor and vice versa." 'Y

A further'objet is the provisionof a c'ontainerj'c'on'sis'tingoftWocoperatingfmenibers togetherffformin'ga Channel *for the resistor, these members beinglm'ova'ble'with respect to each "other along'the-'longitudinal axis'of the resistor, and each -membercarrying a lug or otherimechanical I ne'ansfor exerting'pressure on the resistor, the resistor -being longitudinally compressed by 'relativel Am'otionof'the cooperating members so that every part ofthe resistor isdisturbed by such' relativelnotion. Another object is zthe';1`)i"0v'is'i ')n 'of means whereby thefresistoif 'may bejbroken up into two' or more 'partsin' w'vhclit'he Elongitudinal pressure is transmitted from par-t `='to part thrughout the I'length fdfthe resistor.

'A further'fobje'ctfisgthe 'production of a resistance ne'dium 'of Aizontactin'g aligned resistr blocks Whic'h'peiates at-ate'mperature very little' higher"than 'the temperature de- Sired finthebo'dyl'toibeheated. *Thisis securedby' 'so I'deis'ignimg"'the heatinft'i; 'unit that close material Contact of thehcating element throughout its length i-with'th'e'body which is to be heated is obtained. A further object -isthe construction o'f-an electric` heater, heating rapidly until a definite 'teinp'eratu re is reached.

- With 'the'la'bove 'and 'other objects in view, the i'nve'ritin'lrnay b'e'` said Eto comprehend the eletri'c'ali'heating iunit illustratedin the accompanyingfdraw'ing's l hereinafter described and Vpartcula'rly set l'forth lin `the appended c'laims,`,"together 'with such variations and modifications tlrereo'flas'tvill gbe apparent to one skilled 'in 'the art to which the invention appertains. l

Reference should be had vto the accompanying drawings forming a part of this specifi cation -in which: l I

Figure 1 isa planvieiv of a heating unit in which a portion of the -outercasing is broken away vand shown in section on the line indicated at l-l in Fig. 2.

Fig. 2 is a. section taken on the line indicated at 2 2 lin Fig. 1.

Fig. 3 is a section taken on the line indicated at 3-3 in Fig. 1.

Fig. 4 is a section taken on the line indicated at 4 4 in Fig. 1.

Fig. 5 is a section taken on the line indicated at 5--5 in Fig. 1.

Fig. 6 is a detail view showing one end of the insulator band.

Fig. 7 is a detail view showing the pressure equalizing member used in connection with the variable resistance.

Fig. 8 is a plan view showing the waffle iron to which the heating device of the present invention is applied.

Fig. 9 is a plan view partially in section showing a heating unit of the immersion type to which the invention is applied.

Fig. 1() is a longitudinal section through the heating unit shown in Fig. 9.

Fig. 11 is an end view of the heating unitz F ig` 12 is a sectiontaken on the line 1ndicated at 12-12 in Fig. 9. c

Fig. 13 is a section taken on the line 1ndicated at 13-13 in Fig. 9.

Fig. 14 is a section taken on the lme 1ndicated at 14-14 in Fig. 9.

Fig. 15 is a section taken on the line indicated at 15-15 in Fig. 9.

Fig. 16 is awiring diagram showinga circuit for the electrical heating element usually applied to either of the modifications herein disclosed but for simplicity, illustrated 1n detail only in Figs. 9 and 10.

In Figs. 1 to 8 of the accompanying drawz. ings, the invention is illustrated as applied to a waffle iron in which the heat receiving plate 1, formed of a metal having a high coefficient of thermal expansion and which has high heat conductivity, is provided with an upstanding cylindrical heat receiving wall 2, the interior concave face of which closely overlies the electrical heating element which will be hereinafter described. A cover plate 3 is attached to the upstanding wall 2 by means of screws 4 and at its center to the plate by means of a bolt 5, the cover 3 completing the casing within which the heating elementvis enclosed. The wall 2 has a projecting portion G to which a handle is attached, the inner portion of the handle being provided with a recess S, which communicates through an opening 9 with the interior of the casing for a (purpose which will be hereinafter explaine Mounted within the casing, there is a circula r supporting member mounted to turn on the central bolt 5, and which is of a diameter and thickness at the periphery such as to closel)7 approximate the casing, here being composed of insulating material. This disc has a depressed or channeled peripheral portion in which an electrical heating element may be mounted, the heating element receiving portion of the disc being preferably in the form of two parallel circumferential channels 11, their cross sections preferably tapering .inwardly from the periphery of the member.

For supplying current to the device, terminal clips 12 are attached to an insulating block 13 secured upon the outer face of the wall 2, preferably adjacent the handle, and the clips and insulating block are secured in place by means of binding screws 14, which extendthrough apertures in the wall 2 and which are insulated from the wall by means of sleeves of insulating material extending through the apertures, the inner ends of the screws being threaded into metal electrodes 16 which fit into the Vperipheral channels 11 of the supporting member.

The heating element is in the form of an electrical resistance of the type in which the electrical current is caused to How through a series of contacting resistor bodies which are electrically conductive and whichare held together with a pressure which may be varied to vary the pressure between the individual bodies and to thereby vary the resistance offered to the passage of an electric'current. The resistor bodies are preferably in the fo rm of graphite blocks 17 of trapezoidal form which have a sliding fit in the channels of the supporting disc.

In order to vary the pressureon the-resistance element, means is providedv for imparting a turning movement to the'disc 10 and for transmittingan endwise thrust upon the arcuate rows of resistor'bodies-in the peripheral channels of the disc.v 'The rows of resistor bodies extend lfromithe'felectrodes 16 around a major-portion of Athe.circumferf'ence of the disc, the two channels being separated by an intermediate web 18 throughout the poition of the periphery of thedisc in which the resistor blocks are placed. The web l18, however, is discontinued in the portion of t-he disc to the side of the handle 7 opposite that to which the terminals 12 are mounted inorder to provide a chamber'19 to accommodate the thrust applying devices by which endwise pressure is exerted upon the resist-ance element. The supporting member has an integral web 20 extending across the chamber l19 and on the outer side of this web, there is mounted a metal thrust block 21 which is attached by means of screws 22 to the supporting disc 10. Upon the inner side ofthe web 20 there is a thrust block 23 provided with a knife edge 24, which is attached to the web 20 by screws 25 which are counter sunk into the outer face of the web so that the block 23 is insulated from the block 21. In the adjacent ends of the channels 11 are metal blocks 26 which have flat inner faces engaging the endmost blocks of the resistance element and which have rounded outer faces which are engaged by an equalizing member 27, which is interposed between the thrust block 23 and the blocks 2G in the two channels. The equalizing member 27 particularly shown in Fig. 7

with a boss 32 formed on the wall.

isametallic memberhavingparallel end portions 28 of cylindrical form and with a transverseconnee'ting portion 29 also of cylindrical form. =The cylindrical end portions 28 of the equalizin Y member bear upon the rounded ends ofthe biocks 26 and the cylindrical connecting portion 29 is engaged by theV knife the block 21 and which extends tlirouglrthe wall o fa easing and has threaded engagement The screw 30has aflrnurled head-35 at its outer end by means oflwhich it maybe turned to shift the .disc 10,;about itsA .axis to apply pressure 'through the equalizingmember 27Vto the two resistaneefeleme'nts or to relieve the pressure on the resistance elements, loclenut 3% being provided on the s crew which is engageable withthe boyssg32 tolock the screw in a position lto.,which:it,hasbeen adjusted.

The.resistorbodies extend from the electrodes lGfto the thrust blocks26 and the two resistorelements which are insulated from each other by the web 18 are connect-ed in series-.throughone l.terminal l2 and electrode 16, through the blocks 26 and equalizing member v.27* andit-heJother electrode 16 and its terminal. l Animportantfeatureof the present invention is the provision of a movable supporting element Ifor. theresistanee element which has frietional contact with the rows of resistor blocks` throughout the length thereof, and which carries the pressure applying lug through which endwise pressure is applied to the resistor bodies. -Since the frictional engagement between the supporting member andthe individual resistor bodies insures substantial uniformity in the pressure between the .bodies throughout the length of each of the resistor elements, it prevents inequalities in pressure on adjustment which would otherwise Aimpair the eflicieney of the heating element. T he heat receiving plate is formed of a metal which has a high coefficient of thermal expansion as compared with the resistor blocks and eoacts with the resistor blocks to automatically limit the temperature to which the blocks may be heated by the elect-ric eurrent passing through them. The end thrust on the blocks has an outward component pressingthe row of blocks outwardlyagainst the heat receiving wall so that when the wall expands to a greater diameter, due to the heat supplied thereto from the bloc-lis, the individual blocks will have an outward move- :nent which lessens the pressure between the individual-blocks and automatically increases the ohniic, resistance and cuts down the cin'- rent passing through the blocks.

The outward component of the end thrust on the bloekvsalso servesto vary he .heat convductivity between the resistance element and is rapidly transmitted to the plate. As the n plate becomes hot the thermal expansion lrei lleves the pressure on the resistor bodies reducing the current and the rate at which heat is generated and lessens the pressure between these bodies and the heat receiving wall so sistor-bodies and wall is also reduced, andla substantially constant difference in temperature is maintained between the resistorbodies and heat receiving wall.

An important feature ofthe inventionlis the provision of channels oftaperingz-cross section for the resistor elements and resistor elements of tapered form to,- t inthese channels. The tapered form of channels tendsto cause the blocks to move freely in outward radial direction to maintaincontactwith the concave retaining wall even when the blocks are loose. The taperingchannel .also .cooperates with the tapered blocks to maintain the individual blocks in proper alignment a nd in upright position, the taperingform .of channel preventing the largeronterendsof the blocks from swingingtoward .the bottom of the channel. p

A furtherimportant feature of the invention is the provision of aresistanee element of the contacting resistor body type, which vconsists of two. or more partsarranged with `different lines of vpressure fand mechanically connected so that longitudinal `.pressure may be transmitted from one part to .another throughout the length of the resistor,with the result that substantially equal pressure is maintained in all parts of vthe resistance. This is accomplished by means of equalizing member 27, which serves to balance the pressure between the two rows of resistor blocks, ondwise pressure transmitted from the-electrode 16 through one row of blocks Abeing transmitted through the rocking equalizing member 27 to the otherrow of blocks, thus insuring equal compression at all times in both rows.

A further important feature of thepresent invention is the provision of an insulation suitable for ,electrically insulating the resistance element from non-ferrous heat receiving containing members -sueh as aluminum or its alloys, the insulating means being of such a nature that it readily transmits the heat from the resistance element to the heat receiving body, that is mechanically unyielding, that it may be easily renewed and that it ,responds to the ,thermal expansion of that the heat conductivity between the re- :8'0

lao

the containing member.

This insulation is preferably'in the form of a thin laterally flexible steel band, which is coated on its inner face with a suitable insulating vitreous enamel and which is interposed between the concave face of the vheat receiving wall and the outer edges of the resistor blocks. The band 35 extends throughout the major portion of the circumference of the disc 10 and is provided with elongated slots 36 to receive the insulating sleeves 15 and with an elongated slot 37 to receive the adjusting screw 30. The ends of the band are positioned adjacent Vthe portion of the casing to-which the handle is attached and are provided with heads 38, which have, centrally located projecting lugs 39 which receive pivot pins 40 upon which are pivoted apair of inner toggle links 41, which are pivoted together and to an outwardly projecting rod 42 by pivot 43. A A second pairA of'toggle links 44 are pivoted on the pins 40 and project 1outwardly therefrom, the outer ends of these links being connected by pivots 45 to a collar 46, which is slidable upon the rod 42.

The rod 42 projects into the recess 8 of the handleand is threaded to receive a nut 47. Interposed between a washer 4S on the inner side of thenut 47 and the sliding collar 46 there is a coil spring 49 which exerts an in` ward pressure on the collar'46 andan outward 'pressure on the nut` 47, tending to straighten both pairs of 'toggle links and spread the adjacent endsof the insulating band.v This pressure tends to expand lthe band andl holds the same tightly against'the inner face of 'the'heat receiving walls 2. Suitable pressure may be exerted upon the 'spring 49 by screwingdown the nut 47 and this'pressure is transmitted at all times to the bandl so that it will instantly respond to the thermal expansion of the heat receiving wall. The spring 49 being located entirely within the recess 8 of the handle outside the main body of the casing is protected against the heat generated by the resistor element within the casing and from the heat transmitted to the heat receiving plate which has high heat conductivity so that the spring is not injuriously affected by the heat. l

The cycle of operative changes which the device goes through and which determine its thermostatic property are briefly as follows:

lVhen the device is cold, the aligned resistor blocks will ordinarily be closely confined by the confining means. The resistance of the device being determined by the pressure between the blocks, being low when this is large, a comparatively large How of current ensues and much energy. isdeveloped in the form of heat. The device therefore heats more rapidly than any known heating element of the same working capacity. F or example, a given device designed to operate at 500 watts and set for a temperature of 150 C. may take as much as 4000 watts when cold. This` while a great advantage when thewiring permits, is frequently not desirable when the current supply wires are not fitted to supply so large a current. I often thereforeprefer, as diagrammatically illustrated in Fig. 16, to employ a. series fixed resistance 50 such as nichrome wire or one of the dispersed conductors later to be described, which has the further advantage that it decreases the effective volt age on the variable device per se. And for the reason that excessively large currents are at no time permitted to pass'througli the device, it tends to prevent, over-regulation or hunting. The heat developed heats both element and, by conduction, the containing mcmber, but fheat transfer being made very good the element remains only a few, and nearly constant; number of degrees hotter than the'cont'aining member. Both expand but the containing member expands to a greater degree than the resistor. The initial pressure on thisaccordingly'diminishes, the resistance rises'and less heat is developed. At some point, the energy inflow will equal energy outflow and the temperature of the device will remain constant. If conditions changesueh that'a larger withdrawal occurs, the tempera-ture of thedevice will fall slightly. This causes'the co'ntaining member to contract faster than the element does, the lngitudi nal pressureo'n the blocks being thereby increased and their'resistance accordingly decreases with consequent vincreaseof current flow. Heat will be increasingly developed until the increased heat input 'isequalto'the increased output. It may be arranged so'that the fall of Va degree or :t'wo' may'increase the lcurrent flow several times, though formost purposes a sensitiveness of this grade is not desirable.

It is frequently also desirable that the full possibilities of the device as regards current regulation on the minimum side be not used and I consequently often desire to introduce a fixed resistor in parallel with the variable resistor. This maybe a wire register of the usual type ofnichrome or other resistance material or it may preferably be of a ceramic disperse conductor type such as the resistor 5l illustrated diagrammatically in Fig. 16.

Such a resistor, for example, may be made by mixingY clay or other non-conducting binders such as phenolic resins and the like with more or less of materials which are either originally conductors or become so when subjected to heat. Clay, for example` may be mixed with graphite or some form of amorphous carbon, the whole pressed and fired. Or the carbon may be introduced as any carbon containing material such as dextrose or coal tar pitch and the whole compacted by pressure and then fired. In particular, for the purposes of the present invention, I prefer to lay on to a strip or body of enamehng steel an insulation of vitreous enamel and subsequently overlay this with such a composition as is above described; firing the Whole' to one integral mass. This str1 either vforms the containing expansible mm er oris fixed withinthc expansible member and 'forms the insulating strip in the modification of the invention above described. The variable resistor is dispos'edin close contact with lthis strip as elsewhere described'in this specifi;

cation and such a construction has the' imporl tant further advantagehat the potential' gradient is fixed along the length' ofthe `conductor toa very largeextent, -the electric conduction being everywhere' free between the fixed resistorand'tlefblockscom risingA the variable conductor? l\lov"great di erence' of potential canlever'existibetween vadjacent blocks, novmatter how'defective'the :transmission of pressure from block to bloclr may be. In this form of construction, it is de'- sirable that the conduction edges of the" blocks adjacent the fixed surface of the-:fixed resistance lbe so'n'ewhatbveled away sothat the contactof ea'eh'l'off 'the adjacent blocksV with the fixed resist'orfbe somewhat separated.' In Figs. 9-'to'-15 o'f'fthe'drawingathere is shown amodification ,of th'einvention which in its essentials simplyrepresents a'smallerv arc lof the heating unit-'shown' in 'Figs. 1 i to 8 in' which the-fixed parallel 'and seriesjresis'tance shown'dia'gianim'aticallyfinFig.j v16 are;V employed. The, heating unit :in this i'nodification is of the firm-niersion' type'and the heat receiving and confining-element 'is infthe form ofa longitudinallycurved tubular casy ing52,- which has' aniint'ernallyf'con'cave heat receiving wall 53,1 and a `rmovabl"w'all', vv54 opposite the wall 53, the'fremovablewall'pro viding-*means bywhich the heatingnni't may? be inserted into Orremved'from the casing.'

The heat receiving Wallf 5,3'ha`s a layer of in" sulating material 55'upon its inner face, the insulation consisting` preferablyofa `coating of vitreous enamel, and to the insulated inner face of the wall there is secured the parallel resistance 51 above described.

The heating elementl 57 supporting this modification is of a. form 'to substantially fit' within the walls of a casing, its'curvature corresponding to that of the casing, the heating element being formed of insulating material as in the modificationabove described,

then having an inwardly tapering channel 58 in its convex face, which is closely adjacent the heat receiving wall. A

The length ofithe heating zelementsupporting member is somewhatless than that of the casing and the supporting member isA t mounted to slide in the casing beneath'the channel 58. The supporting member is provided with a longitudinal aperture 59 through which the series resistance" extends. Ags in the modification first described, the variable C5 resistance consists of a row of the' tapered re- 57'is provided with alli'ig 61 extendingv i'nto` 75 the'channel 58 adjacent theued thereof opp'o';l

site'that 'in which thefelectro'de 60 engages.' and attached to: thein'nerface of'this'-lug there v'ist a metalblock'oi :electrode 62' 'whichT engages the endmost resistor blockv in theI channel :sothat 'when the supporting 'element the row'of'resistorblocks'lInthis mii I cation, as jwell as in the'modification fi'r's't 4deis moved endwis'e', pressure 'is'lexerted 'ii'ion scribed, the-'blocks' 'are maintained: alignment and in upright position` b'y :their .Y engagement with the ktapered channe'l'and uniform pressure is' Vobtained throughout :the

iength of the' mai-0f .blacks-by ,the fific'iionai 2 engagement l'of the :bodily: movable 'supportingv member' with the blocksthroughout the Ilected leans :of b

the lug 6l and zwith a leads to a terminal postv vca'rriedbyj casing' and suitably insulated therefrom@ QAsecondten miaiiposteefis" mourf'd adja enc pest-'65 and fisConnected-liauijaajaeiitii Qffthejj series resistance 50which isfconneeted atI its opposite end vbyga scr'ew' 6 '7`to th'eelectrode" 60, so that cu'rrentsupplied through the termi-v nals and 66 passes'through the Are'4 sistance I51 .andi variable" resistzinte 17j vin parallel `and throughl the' "fixed" series resistance50-f4 :I 4 i For adjusting supporting.member` 5'( in,

the'casing, a screw` 68: is'p'p'rovided which" is, threaded into a 'metal block 69 secured in one end A of the member: 5'( and which' extends through an apertureOin 'the end wall of thc 'ca-sing. The projecting'end ofthe lscrew is provided with a parallel head by means of which it may be adjusted to move the sup'- porting member in 'thecasing and vary the pressure exerted endwise uponp'the row of blocks', the aperture 70: vbeing slightly larger than the screw to permit'the slight angular movement of the `screwre s ulting from the movement 'of the supporting member."

In this modification, as well as the first, the confiningiand heat vreceiving member has 'high heat'eonductivity and has 'a high coefficient of thermal eiipaiision'.'y The 'insulation andthe dispersed,resistancefelement interposed between theca'rbon blocks of the variable resistance and thej'heat receiving wall readily transmitthe ,heat from the main resistanceelement to" thefwall, so that the heat receiving bodyquicklylabsorbs heat from the heating lelement and only 'a Vsmall differllO ence in temperature is required between the heating element and heat receiving body.

In both modifications, the heat receiving and retaining body, by reason of its high coefiicient of thermal expansion, and by reason of the engagement of the heating element alon a concave face o f the heat receiving bo y, serves to automatically relieve the pressure between .the individual blocks of the variable resistance element, increasing the resistance and cutting down the current so that the temperature to which the resistor blocks. may be raised ismaintained .at all times below the temperature at which the blocks be injuriously affected-by theheat. In both modifications, the outward-component 'of the end thrust .on the row of blocks composing the resistance element serves to maintain the resistanceelement at all times in close contact with the heat,reeiving..wa1l and zto maintain effective heatgtransmitting relation thereto. Y f

Furthermore, is teh@ understood that the particular formsofapparatusshown and described, and the particular' procedure set forth, arepresentedfor purposes of explanation andillustration aiidjthat,various modifications of said. apparatus .and .procedure can be madewithoutzdeparting from my-in-l vention asdefined in the-appended claims.

1. An electrical unit-comprising aA resistance element composed Aof j contacting electrically cond,u'ctive,resistor 4bodies, confining means electricallyfinslilated from; said resistor bodiesalid displosedfin 1heat receiv mg relatlon thereto, saidifonfimng means2 having a coefiicient o f thermal expansion relatively highv aseoinparedctothat of :saidAA resistor VbodiesA and adjustable pressurev :ip-

plyingA means engaging gone.. endlof 'the resistance elementand having .a part in contact withV the resistance *elementfthroughout the length thereof. A ,n v l 2. An electrical heating ,unit comprising a resistance element composed ofcontacting electrically conductiveresis'tor bodies, a casing for said resistanceelement having a heat receiving wall `clos ely,adjac'ent said resistance element, a support for said resistance element movably mounted in the casing and having a channel to receive said resistance element, a member cnrriel'by thecasing engaging one end of the resistance element, a member carried by the support engaging the opposite end of the resistance element and means for shiftin said member in the casing to apply enc wise pressure to the resistance element.

3. In an electrical heating unit, in combination.` a substantiallyy curved expansion member, a resistance element composed of a series of aligned resistor blocks disposed closely adjacent said expansion member on the concave side thereof and closely following the concave curvature thereof, said expansion member having a relatively high coefficient of thermal expansion with respect to' that of said blocks-said blocks being electrically insulated from said expansion meinber, a fixed lufr secured to said expansion member and abutting said series of' blocks at one end thereof, an electrically non-conducting co-operating member arranged to contact with said blocks and movable along the longitudinal axis of the series of resistor blocks, a lug secured to said cci-operating member arranged to abut said series of blocks at the other end thereof, means for slidably adjusting said co-operating member relative to said blocksand maintaining said co-oper` ating member in desired adjusted position, said longitudinal pressure heilig variable with the expansion and contraction of .said expansion member due to heatreceived from said resistor blocks, and-means for supplying currentto said resistance element to heat said blocks.

4. An electrical heating unit comprising a casing having an internally concave heat receiving wall, n member mounted within the casing having :in-external convex curvature substantially conforming to the curvature of said wall, said member having a channel in its :outer face, va resistance element interposed between said movable member and walland seated in said channel, said resistance clement beingcomposed of contact-ing electrically conductive resistor bodies, a layer of-material having electrical insulating and heat conducting properties interposed hetween said resistance element and heat receiving wall, a lugfixed with respect to the wall engaging one end of said resistance ele ment, aj lug fixed with respect to the movable member engaging the opposite end of the resistance element,l and means for moving said member along the wall to vary the pressure between said resistor bodies.

5. An electrical heating unit comprising a casing having an internally concave heat receiving wall of high heat conductivity, a member in the casing having an outer face conforming to the curvature of the heat receiving wall and closely adjacent thereto, said member having au inwardly tapering channel in said outer convex face, a resistance element in said channel composed of a row of contacting resistor bodies of tapered form fitting in said channel, a heat conducting insulation interposed between said resistance element and casing wall, means for applying an endwise pressure to said row of bodies, and means for supplying an electric current to said resistance element.

6. An electrical heating unit comprising a heating unit having a supporting member provided with a convex face, said supporting member having an inwardly tapering channel in its convex face, a resistance element composed' of; contacting' electricallyA` conducting resistor 'bodies' oftapering 'form fitting in saidchannel, an outerheatreceiving casing of'highh'eat conductivityand'havl ing -a Vthermal coefficient'of expansion-'Telai rentt'o'said resistance element;`

r forff'applying endivise pressure'- ,simultaneously to 'said'rows of blocksg-means for* equali'z'ing` theI pressure e'x'erte'd onN saidv bodies and 'fr"transmitting pressure from 1 one row'of bodies to the other,VA a casing havf f ingfa'heatreceiving2 portion of 'high'V heat conductivity closelyadjacent "said resistance elements 'and insulated Ttherefrom, andV means for supplying current Yto'said resistance ele'-4 ment."

8. An electrical heatingjunit comprising a resistance f element coinpose'd" of"contacting electrically conductive *resistor bodies i arl' ranged in 'a plurality' of separate rows; side" by side, ay casing having high =heat "condito-'- tivity and a high thermal coefficient "of f'eX-- pansion relativeftoy said resistor' blocks: sai-d casing having'"a'vvallfdisposedffiiifconfining1 relation/closely'adj avcent said'blocks' and'insu lated therefrom',membersircd'to the casing" engaging the `ends 'of'sai'd'rows ofcontacting elements at one end',`means for applying pres-1 sure to said rows of-bodiesat the opposite" ends thereof, lsaid pressure*applying means' including means for equalizingthepressure-` transmitted to saidA rows of blocks :and: for' transmitting pressure fromone row to'anl"l other, and means `for supplying 'current "to" said resistance element.

9j An electrical heating unitcomprisin'g" an internally concave heat receiving element,'

a resistance element composed of a seriesfof L contacting electrically conductive resistor bodies, a. laterally flexible insulating member of non-compressible material interposed be:- tween the heat receiving element andthe rel sistance clement engaging and conforming" to the concave wall of the heat receivingele-- ment, and means for applying pressurefto' said resistance element.'

10. An electrical heating unit comprising a resistance `element composed of a series of contacting electrically` conductiveV resistor" bodies, acasing for 'said resistance 'element' f having an internally'concave heat receiving '1 Wa'llg a lrelatively' thintransverselyi flexible f insulating member interposed between the re'- sistance-'elementfand Wall,A means for exerting pressureon said insulating vmember tomaintain the f samel in' 'engagement with' the casingw'all, andmean's for `applying endwise 70 pressure-to said lresistance elementi and for maintaining the sam'ein'contact -through'out f its length with' said insulating member.

l1; A'n electrical heating 'unit comprising. af'casing having anfinternally'concaveheat're 75.- ceivingfvall, al resistance' element composed of'a series ofcontacting'electrically "conductive 'resistory bodies and having 'longitudinal curvature' lcon forming to-'the curvature of the Wall; afthin'ftransversely flezrible-- expansive 80' insulatings band :interposed betiveen the*re sistance element; and' heat 'receivingl wall,`-' and 'means' for exerting "end'visepres'sure'ion said-"band and on said iresistance'v element I'to f press the band 1outivardlyfagain'stsaid'v Wall 7 e5I and" said* resistance @element-f'- outwardly' againstsai'd band?" -`f 12.' An electrical lheatingu'nit comprising at casing `having an internally LJcOnCaVeMhe'at receiving `wall' which" hasa relativelyA high f o0A v teinperatureicoeiicient of expansion, a thinv` transversely `flexible' expan'sibleelectrically insulating -and heat conducting1 bandV "eng'agil ing' and conforming 'tof said concave Wall, means for maintaininga pressure on" the -ends1 95-` of said band to maintain the same in engage* ment fw'ithfthe jw'all; resistance elrnentecomposed of f contacting electrically' conductive* resistor bodies-"alor'rg th'einner 'side of said ir'isulatingv band; and-*adjustable means "for 100 applying endwisepressure't" said lresistor element to rn'aintai-n'theEsame in contact'with said band? I 132' An' electrical heating :unit `comprising f a casing 7havingaan 'ntrnallyconcave' heat' 105 receiving# wall, a 'member movably mounted withinthe casing' which has Yan Vouter face conforming to the .curvature of 'the heat re'- ceivingfwall and4 1Iclosely/adjacent` thereto; a plurality-'of channels extending'along 'said 11o outer face'vofsaid' member, resistance'elements `in said channels -eachcomposed of a series ofl contacting resistor 'blocks',' m'eans" insulating said Yresistorel'em'ents from said heat receiving'wa'll, lugs fixed tosaid heat 115 receiving'aval'l and' engaging'f'said resistance elements at one end, means for moving'said member V'along said wall, means interposed between said movable 1member"andresistance elements' at'the end opposite that engaged by 120 the-'fixed lugs for' simultaneously applying endwise'pressure to said resistanceelements, and means for supplying current tosaid resistance' elements.'

14." AnV electrical heating unit comprising 125 acasing V'having an internally concave heat receiving wall,'a member movably mounted Within 'the-'casing which has'anouter face conforming to the 'curvature of the Lheat ref ceivinglwvall 'and closely ladj acentthereto, 'a '13@ plurality of channels extending along said outer face of saidv member, resistance elements in said channels each composed of a series of contacting resistor blocks, means insulating said vresistance elements from said heat receiving Wall, lugs lixed to said heat receiving wall and engaging said resistance elements at one end,y means for moving said member along said Wall, means interposed betweensaid movable member and resistance elements at the end opposite that engaged by thefixed lugs for simultaneously applying endwise pressure to said resistance elements, said pressuret applying means including means foi-equalizing the pressureon said re` sistance elements, :and means for supplying current .to saidresistance elements.

A15. Anelectrical heating unit comprising aninternally concave .heat receiving element, a -relatively t liin. metal band coated with insulating .ena`rriel,` engaging Athe concave wall of the heat receiving element, means connectedxto thecenldsof saidlfband Ato apply end wisc pressure theretogt'o maintain the same. in close contact ..with .said Wall, a resistance element engagingfthe inner face of said band andwcomposedzof a royvof .contacting electrically ,conductingg resistor blocks, means orV applying .endviiisle'pressure to said resistance l element; and means. for"v supplying current f 1. r' I6, electrical. heal ing unit comprising messinese. element compesd.- of@ row of contactinfrrelectrically conducting resistor blocks, assiippprtior lsaid-.element having av convex face-providedVwithgafchannel ini-Which Said-:element is mounted, a .thing insulating band of laterally flexible incompressible ina.- terial,.engaging ,the outer side of. said resistance element, acas'ing having. a heatireceiving portionof relatively vhigh temperature coellicient of expansion -.as compared to said blocks, said heat receiving portion of the casingliaving a concave Wall substantially conforniingtofand. closely adjacent the convex face ,of saidsi'ippor'meansor applying endwise pressureto said resistance element, a spiing connected. to said band. to exert endwise pressure;l thereon to 'maintain the same in contact alongsaid heat receiving wall, and means for supplying current to said resistanceeleinent.

17. An electrical heating unit comprising a resistance element composed of a row of contacting electrically conducting resistor blocks, a support for said element having a convex face provided with a channel in which said element is mounted, a thin insulating hand of laterally flexible incompressible material, engaging the outer side of said resistance element, a casing having a heat receiving portion of relatively high coellicient of thermal expansion as compared to said blocks, said heat receiving portion of the casing having a concave wall substantially coniufr body, and means for supplying current to g said resistance element. I

1S. An e ectrical heating unit comprising a heat receiving body vhaving a cylindrical wall, a supporting member of insulating material fitting Within said cylindrical Wall and mounted to turn about .a central axis; said supporting member having @channel-along. its circuniferentialface, aresistance element composed oa row of contacting electrically conducting resistor. blocks iseated i 4 saidj channel). a lug vfixed to. thecasrng-engaging,

one endl of said .resistanceelement7 means .for.

moving. .said `supporting.member fabolitllits g a xis, 4means interposed between; said support-` ing ineinber and the.,oppos iteend.of the resista-:ice element to applyendwisepress'ure to the resistance element; insulating means;in. tcrposed between' the blocks :andi said .eyliii-.j urical wall, and means for supplying current inn:

to said resistance element.

` 19. An .electrical Heating heatreceiving:bodyhaving aP cylindrical Wall; .5 a supporting-member ofinsiilatinginateiial-x ittng.v within jsaidTj {cylindrical-wall and; mounted A`to turiiabout-:aicentr-al axis, saidf supporting' member having a channel along itsE circumferential face, a resistance. element l composedlof a row. of contacting. electricallyt conducting resistor blocksseated `iiijsaid channehalug fixed to the .casing ei igagin, i;H

one end of said resistance element, means for moving said supporting .-memberabout its axis, means interposed between said supporting member and the opposite end ofthe resistance element to apply endwisepressure to the resistance element, a thin insulating -band interposedl between the resistanceelement and cylindrical Wall, a spring mounted outside said .cylindrical wall and connected `to the ends of the band to exert an expanding pressure on the band, and means for supplying current to said resistance element.

20. An electrical heating unit including a variable resistance element comprising a row of contacting-electrically conducting resistor elements and means for applying endwise pressure to said row of resistor elements, a fixed resistance in parallel with said variable resistance, and a second fixed resistance in series with said variable resistance 2l. An electrical heating unit comprising a variable resistance element comprising a row of contacting electrically conducting resistor elements and means for applying endwise pressure to said row ofresistor elelsinai a;

ments, a heat receiving body in close proximity to the outer side of said variable resistance, and a resistance element ofthe dispersed ceramic type connected in parallel with the variable resistance and interposed between said variable resistance and said heat receiving body.

22. An electrical heating unit comprising a Variable resistance element comprising a row of contacting electrically conducting resistor elements and means for applying endwise pressure to said row of resistor elements, a heat receiving body in close proximity to the outer side of said variable resistance, a resistance element of the dispersed type connected in parallel with the variable resistance and interposed between said variable resistance and said heat receiving body, and a fiXed resistance extending along the inner side of said variable resistance and connected in series therewith.

23. An electrical heating unit comprising a variable resistance element formed of a series of contacting electrically conducting resistor` bodies, means for varying the resistance of said element, and a second resistance element arranged in parallel electrical relation with the variable resistance element and electrically connected to certain of the intermediate resistor bodies.

24. An electrical heating unit comprising a variable resistance element formed of a series of contacting electrically conducting resistor bodies, means for varying the resistance of said element, and a second resistance element arranged in parallel electrical relation with the variable resistance element and electrically connected to the variable resistance element at a plurality of points intermediate its ends.

25. An electrical heating unit comprising a resistance element composed ot a series of contacting electrically conductive resistor bodies, a casing for said resistance element having a heat receiving wall closely adjacent said resistance element, a support for said resistance element movably mounted in the casing, said resistor bodies being mounted between said casing and said support and held in alinementby one of them a member carried by the casing engaging one end of the resistance element., a member carried by the support engaging the opposite end of the resistance element, and means for shifting one of said members to applyv endwise pressure to the resistance element.

In testimony whereof I affix my signature.

STERNE MORSE. 

